Supporting structure for an open-space photovoltaic system

ABSTRACT

A supporting structure for an open-space photovoltaic system with several ground supports arranged in at least two mutually parallel rows oriented in essentially North-South direction and installed vertically in the ground, with beams supported on free ends of the ground supports located at the same location along a row, and with module rails attached to the beams for attachment of fastening means for photovoltaic modules. The module rails are secured on or between two corresponding adjacent beams in essentially North-South direction. The free ends of the ground supports are positioned at the same height above terrain ground, so that the beams and the module rails extend essentially plane-parallel to the terrain ground. This arrangement reduces material consumption, and only a small surface area of the supporting structure is effectively exposed to wind gusts. Each row of ground supports includes ground supports with both rigid and flexible flexural characteristics.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2009 024 738.6, filed Jun. 12, 2009, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

The invention relates to a supporting structure for an open-space photovoltaic system with several ground supports with one end rising from the ground, with beams being supported on the other end, and with module rails mounted on the beams for attachment of fastening means, in particular clamps, for photovoltaic modules.

The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.

Supporting structures of this type are widely used. They have mostly a superstructure where ground supports of different lengths rise vertically from the ground or are embedded vertically in a foundation connected with the ground. The ground supports are arranged in two rows, with the row with short ground supports and the row with the longer ground supports both extending in East-West direction. Beams or joists are placed on top of the free ends of the ground supports, which also oriented in East-West direction, and attached. This produces two continuous beams having a length of, for example, hundred meters, which are each supported by a plurality of ground supports. One of the continuous beams is at a lower level than the other, with a typical height difference ranging from, for example, 60 cm to 80 cm. The height difference defines the slope of the module rails, which extend perpendicular to the supports and are mounted thereon in North-South direction, with respect to the ground plane. The photovoltaic modules all then attached on the module rails with clamps.

This arrangement provides an advantageous angle of incidence for the photovoltaic modules, but is relatively complex and relatively massive, in order to be able to withstand wind forces which attack below the mounted inclined PV modules. Moreover, automated installation of the PV modules is difficult due to the large inclination. In addition, in an arrangement with several rows, space must be left between the rows to prevent shadowing of the lower region of the adjacent northern row of PV modules by the upper photovoltaic modules of the adjacent southern row of photovoltaic modules. Finally, ground supports and beams cannot be used for dual purposes where a row of beams supports module rails for two rows of photovoltaic modules, as this is not possible due to the aforementioned required spaces between the rows and the different levels.

It would therefore be desirable and advantageous to obviate the aforementioned disadvantages associated with the massive structure and the space requirement, to provide an improved supporting structure for a photovoltaic system which facilitates automatic installation of the photovoltaic modules and reduces oscillations caused by the wind load by transferring the associated wind forces into the ground.

SUMMARY OF THE INVENTION

The present invention resolves prior art problems by arranging at least two mutually parallel rows having each at least four ground supports in substantially North-South direction, installing a corresponding beam in substantially East-West direction on or between ground supports located at the same position along a row, mounting at least one module rail on or between two corresponding adjacent beams in substantially North-South direction, wherein the other ends of the ground supports are located at the same height above the ground, so that the beams and the module rails extend substantially plane-parallel to the ground, wherein each parallel aligned row of ground supports disposed at the same position in the row has ground supports with a comparably rigid flexural characteristic, and wherein at least two comparatively flexible intermediate ground supports are located between each of two consecutive ground supports with rigid flexural characteristic.

This arrangement allows installation of the photovoltaic modules without requiring a large area; however, because the photovoltaic modules extend parallel to the ground, the light efficiency is reduced.

The reduced light efficiency can be compensated in part by installing the photovoltaic modules on the module rails with an angle of inclination between 2° and 20°. Advantageously, the angle of inclination may be provided by the type of the fastening means. For example, clamps may be employed which support the lower edge of a photovoltaic module on a support surface which is located at a lower level than the upper edge of the preceding photovoltaic module which rests on the clamp on a support surface at a higher level. Such clamps are commercially available for use with system installed on flat roofs.

A large facility dimensioned according to the invention with a rectangular design may have edge lengths of several hundreds of meters, which may introduce substantial forces under windy conditions or may even cause oscillations. The substantial forces are counteracted according to the invention in that each parallel aligned row of ground supports at the same position in the row has a comparable rigid flexural characteristic, and two comparatively flexible intermediate ground supports are located between two corresponding consecutive ground supports with the rigid flexural characteristic. A portion of the forces is then advantageously transferred through flexing of the intermediate ground supports into the ground as a bending moment, while only fixed points are defined to prevent excessive flexing. A buildup of oscillations can be counteracted with springs, as described below in more detail.

The supporting structure described above represents the smallest unit exhibiting the advantages of the invention. In practical application with large photovoltaic systems extending over several hundred meters and having areas of up to 1 km² equipped with PV modules, the smallest unit can be easily expanded or multiplied. The smallest feasible lower dimension to justify the costs for construction vehicles, installation automat, personnel, etc., appears to include at least four mutually parallel rows having each at least four ground supports and accordingly four beams. The term “beam” in the context of the present invention refers to any support member capable of supporting module rails. It is also not required that a corresponding dedicated, separate beam is mounted on or between two grounds supports. The beam may be dimensioned to extend across several ground supports. Accordingly, only a portion of the beam is then located between two grounds supports.

As mentioned above, large areas of contiguous metal may be accumulated in an area, which would represent an attractive target for lightning strikes during a thunderstorm. Accordingly, the entire metal mass is advantageously subdivided into a large number of small, mutually insulated metal masses, which then no longer form a large “striking electrode” for a lightning bolt. This is accomplished by fabricating at least one of the parts: ground support, beam, module rail, or fastening means from an electrically insulating material. Alternative or additional measures provide:

-   -   that the ground supports and the beams are made of metal and         that an insulating material separates the beams from the ground         supports, and/or     -   that the beams and the module rails are made out of metal, and         that an insulating material separates the module rails from the         beams, and/or     -   that the fastening means is made of an electrically insulating         material.

The aforementioned different flexural characteristics can be due to the cross sections of the ground supports. For example, the ground supports may be round pipes having different diameters, wherein the rigid ground supports have a greater diameter than the flexible ground supports. IPE or a wide-flanged-I-beams can also be used as ground supports, which can be installed in the longitudinal or transverse direction depending on the desired flexing direction. The terms “rigid” and “flexible” are meant to indicate relative properties and do not represent a limitation with respect to the physical value of the flexural characteristic.

Advantageously, the rigid flexing direction for the intermediate ground supports extends in the East-West direction and for all other ground supports in the North-South direction. This is related to the later installation of the module rails which are tensioned. The rigid flexing direction of the intermediate ground supports in the East-West direction prevents excursions at great lengths which could cause the PV modules made of glass to push against each other. However, the ground supports may also be installed with the directions reversed or even in arbitrary directions.

To simplify their fabrication, the module rails are provided as bands or cables with a ready-made length and have on at least one end a spring element—preferably in conjunction with an isolator. Several of these ready-made module rails are then connected with one another via the spring and optionally the isolator. This preparation of the module rails reduces the complexity of installation on-site, which is more expensive than at the place of manufacture.

To simplify installation, the ground supports may be arranged in a grid pattern, wherein the module rails in this grid pattern are provided with preparation means for preparing their attachment to the beams. The preparation means is in its simplest form an opening or a hole extending through the module rail, through which a screw can later be screwed into the beam for affixing the module rail on the beam.

The module rails are typically made of aluminum profile. Alternatively, to shorten the installation time, the module rail may advantageously be a flat steel band, wherein the spring is realized by corrugating the flat steel band at an end.

A height of the beams or joists of 0.5 m to 1.5 m above terrain ground, i.e., above ground level, has proven to be sufficient in the context of the stated object to achieve a low installation height of the supporting structure.

According to a possible method of the invention for installing the supporting structure, the ground supports are first fixedly installed in the ground so that their free ends are all approximately at the same height and several parallel adjacent rows are formed, whereafter the beams are connected with the free ends of the ground supports which are located next to one another at the same position of the rows. In an additional step, the module rails are attached on one end and tensioned by applying a tension force at the other end, whereafter they are attached on the beams in the tensioned state. This approach requires that the module rails are made of at least a flexible material, for example the aforementioned flat steel, or even made of a flexible material, such as nylon or Teflon band, which then has an integrated spring action. The band which is attached with one end to the beam on the rigid ground support is tensioned with a cable winch until all openings are located at the height of additional beams. The band is then affixed in this position to the beams through the holes.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 is a top view onto a supporting structure for a photovoltaic system,

FIG. 2 is a longitudinal section taken along the line II-II in FIG. 1,

FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1,

FIG. 4 is a perspective view of an open-space photovoltaic system,

FIG. 5 shows a single row of the system of FIG. 4 according to the invention,

FIG. 5 a is a detailed view of a cross-section of a ground support, wherein the ground support is rigidly installed in the N-S direction,

FIG. 5 b is a detailed view of an intermediate ground support cross-section, wherein the ground support is flexibly installed in the N-S direction,

FIG. 6 a shows a beam with a module rail before tensioning, and

FIG. 6 b shows a module rail affixed on the beam after tensioning.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIGS. 1 to 3, there is shown a supporting structure 1 having two parallel rows 3 a, 3 b of ground supports 5, 5′ which are embedded in the ground 13. The ground supports 5, 5′ are either directly pile-driven into the ground or connected with the ground by way of a foundation (not shown). In both situations, a fixed support for the ground supports 5, 5′ is provided on the ground level.

The rows 3 a, 3 b are oriented in the terrain in North-South direction N-S and connected at their upper, i.e., free, end to joists or beams 7. These are only schematically indicated in FIG. 1 by a line. According to FIG. 3, the connection can be provided by resting the beams 7 on the end face of the ground supports 5, where they are then attached (not shown in FIG. 3). Alternatively, the beams 7 can also be connected with unillustrated beam saddles, so that the upper end the face of the ground supports 5 forms a flush surface with the top side of the beam 7. In both situations, the unsupported distance between the ground supports 5 is bridged in the East-West direction E-W, i.e., two corresponding ground supports 5 located at the same location in the row 3 a, 3 b are connected with a beam 7. The first beam 7 hence connects the first ground support 5 of the row 3 a with the first ground support 5 of the row 3 b. The following beam 7 then connects the second ground support 5 of the row 3 a with the second ground support 5 of the row 3 b, etc.

According to FIG. 2, beams 7 with a U-shaped profile may also be used. Conventional fastening means 10, for example clamps, are arranged between the individual beams 7.

At least two module rails 9 adapted to receive or support several photovoltaic modules 11 are installed on the beams 7 in mutually parallel relationship in the North-South direction N-S. With this arrangement, all module rails 9 are located in a plane extending plane-parallel to the ground 13.

FIG. 2 thus shows a variation of FIG. 3: the beam 7 is here not a massive beam, but rather a beam with a U-shaped profile, wherein the web of the profile rests on the end face of the ground support 5.

FIG. 4 shows a detail of a photovoltaic system (PV system) for open-space installation, which includes four rows 3 a, 3 b, 3 c, and 3 d of ground supports 5. A minimum of two rows is required. A beam 7 is installed from one ground support 5 to the next ground support 5, wherein each row 3 a to 3 d includes a continuous a module rail 9, similar to a model railroad. Alternatively, beams 7 may span a greater distance than the distance between two ground supports 5, so that not every ground support 5 has joints. For example, correspondingly longer beams 7 may abut only at each second or third ground support 5. In FIG. 4, each beam 7 has eight module rails 9, which extend in the North-South direction and in the illustrated example support four adjacent PV modules 11.

As shown in FIG. 4, these photovoltaic modules 11 are installed on the module rails 9 at an angle of inclination of, for example, between 2° and 20°.

FIG. 5 shows a strip of the described PV open-air system, showing sequentially two ground supports 5 located at a first position of their respective row 3 a to 3 b. The eight module rails 9 arranged next to one another on the beam 7 are each implemented as flat steel tape, which extends continuously across a large portion of the supports 7. The length of the module rails 9 in form of the flat steel tape is limited only by the ease with which the spool on which the flat steel tape is delivered can be handled. A spring 15 is located on at least one end of the flat steel tape. The spring 15 is most easily formed by a corrugation in the flat steel tape. In the illustrated exemplary embodiment, a spring 15 is provided on adjacent ends of consecutive module rails 9. A (symbolically indicated) connecting element 19 joins the two flat steel bands with each other at the joint 17.

A corresponding isolator 21 (see FIG. 6 a, 6 b) which electrically insulates the connected module rails 9 from one another is arranged before each spring 15. Such isolators 21 are known from overhead transmission lines and are used in the present application to avoid a long, continuous, electrically conducting metal mass. This is viewed as a cause for an above-average risk for lightning strikes in PV open-air installations. The isolator 21 can be omitted if a module rail 9 is made of an electrically insulating material.

FIG. 5 also shows detail circles to the FIGS. 5 a and 5 b, which illustrate the orientation of the installed wide-flanged-I-beams (or other IPE-beams) as ground support 5. FIG. 5 a shows a cross-section through a ground support 5 which is fixedly oriented in the N-S direction and in which the module rails 9 extend. If forces develop that act in this direction, then these forces are absorbed by the ground support 5 and partially dissipated into the ground.

The detail circle of FIG. 5 shows the ground support 5 as installed as an intermediate ground support 5′ which is located between two ground supports 5 that are rigid in the N-S direction. This ground support 5 is referred to as intermediate ground support 5′ and is identical to all other ground supports 5, but has a different installation orientation. The wide-flanged-I-beam of the ground supports 5 operating as intermediate ground support 5′ is installed with its rigid flexural characteristic in the E-W direction, whereas its more flexible flexing direction is oriented in the N-S direction. In the illustrated embodiment, two intermediate ground supports 5′ a located between two corresponding ground supports 5. If a joint 17 is required, then this joint 17 is preferably located between the two intermediate ground supports 5′.

Alternatively, the ground supports 5 may be round pipes with different diameters, wherein the rigid ground supports 5 have a greater diameter than the flexible ground supports 5′.

A method for installing the supporting structure 1 is described in more detail with reference to FIGS. 6 a and 6 b. The ground supports 5, 5′ and the beams 7 are introduced into the ground in a conventional manner, until they are plane-parallel with respect to the ground 13. The flat steel forming the module rail 9 is then unwound from a spool (not shown) and placed onto the beam 7, so that the module rail 9 sags between the beams 7—similar to an overhead transmission line. FIGS. 6 a and 6 b also show that the module rail 9 has an opening 23 which is located in FIG. 6 a noticeably beyond and to the left of the center of the beam 7. The beam 7 is here constructed—as viewed in cross-section—as a pot-shaped metal part, with an inner pot bottom abutting the free upper end face of the ground support 5. Before the module rail 9 is unwound and positioned, it is attached to a ground support 5 (not shown in FIG. 6 a) which is rigidly installed in the N-S direction. The result is the illustration of FIG. 6 a, where the opening 23 is located to the left of the beam center. A winch is connected to the unattached end of the module rail 9, which pulls the module rail 9, which is attached only at the left side, in the direction of the arrow 25.

The winch is operated until the module rail 9 is tightened to a point where all openings separated by the same spacing as the spacing between the beams 7 are located on top of the respective beam 7. This position is illustrated in FIG. 6 b for a beam 7 positioned with one of its ends on the right. The module rail 9 is then affixed on the beam 7, for example with a conventional screw-nut connection 27.

FIGS. 6 a and 6 b further illustrate a first insulation means 29 which electrically insulates the module rail 9 from the beam 7. Also shown is a second insulation means 31, which electrically insulates the beam 7 from the ground support 5. Both measures are intended to prevent large, electrically contiguous masses of metal to reduce the risk of a lightning strike.

In summary, a supporting structure 1 for an open-space photovoltaic system is advantageously provided, which has several ground supports 5, 5′ which rise at one end from the ground, with beams 7 resting on the other end, wherein module rails 9 are secured on the beams 7 to which then fastening means, in particular clamps, for photovoltaic modules 11 can be attached. The ground supports 5 form at least two aligned rows 3 a, 3 b having each at least three ground supports 5 oriented it essentially North-South direction. A corresponding beam 7 is installed substantially in the East-West direction on or between ground supports 5, 5′ disposed at the same position in the row 3 a, 3 b. At least two module rails 9 are attached on or between two respective adjacent beams 7 in essentially North-South direction. The other ends of the ground supports 5, 5′ are at the same level above terrain ground 13, so that the beams 7 and the module rails 9 extend it essentially plane-parallel to the terrain ground 13. This arrangement enables an effective installation with little material consumption, and the supporting structure 1 exposes only a small effective surface area to wind gusts. Each row 3 a, 3 b of ground supports includes ground supports 5, 5′ with partially relatively rigid and flexible flexural characteristics.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A supporting structure for an open-space photovoltaic system, comprising: a plurality of at least four vertical ground supports arranged in parallel aligned rows and having defined positions along a row, each vertical ground support having two ends, with a first end installed in the ground, a plurality of beams supported on a second end and positioned at an identical height above terrain ground, with each beam installed on or between ground supports located at identical row positions along the rows, and at least one module rail secured on or between adjacent beams and configured for attachment of fastening means adapted to receive photovoltaic modules, wherein the plurality of beams and the at least one module rail extend essentially plane-parallel to the terrain ground, wherein each row of ground supports comprises ground supports with a comparatively rigid flexural characteristic located at identical positions in the rows, and wherein at least two comparatively flexible intermediate ground supports are located between two consecutive arranged ground supports having the rigid flexural characteristic.
 2. The supporting structure of claim 1, wherein the photovoltaic modules are mounted on the module rails with an angle of inclination between about 2° and about 20°.
 3. The supporting structure of claim 1, wherein at least one of a ground support, a beam, a module rail or a fastening means is made of an electrically insulating material.
 4. The supporting structure of claim 1, wherein the different flexural characteristics are based on cross sections of the ground supports.
 5. The supporting structure of claim 4, wherein the ground supports comprise round pipes having different diameters, wherein the rigid ground supports have a larger diameter than the flexible ground supports.
 6. The supporting structure of claim 4, wherein the ground support is an IPE or a wide-flanged-I-beam, which can be installed longitudinally or transversely, depending on a desired bending direction.
 7. The supporting structure of claim 6, characterized in that a rigid bending direction of the intermediate ground supports is oriented in an E-W direction, while the rigid bending direction of all other ground supports, excluding the intermediate ground supports, is in an N-S direction.
 8. The supporting structure of claim 1, wherein the modular rails are bands or cables having ready-made lengths with ends, the modular rails comprising a spring disposed on at least one of their ends.
 9. The supporting structure of claim 8, wherein several module rails are joined with one another via the spring.
 10. The supporting structure of claim 9, wherein several module rails are joined with one another via an isolator.
 11. The supporting structure of claim 1, wherein the ground supports are arranged in a grid pattern and the module rails include openings configured for attachment to the beams.
 12. The supporting structure of claim 8, wherein the module rail comprises a flat metal band and the spring is implemented as a corrugated section disposed on at least one of the ends of the flat metal band.
 13. The supporting structure of claim 1, wherein the plurality of ground supports is aligned in rows oriented substantially in the North-South direction, wherein the plurality of beams is aligned substantially in the East-West direction, and wherein the at least one module rail is aligned substantially in the North-South direction.
 14. The supporting structure according of claim 1, wherein the plurality of beams is located at a height of 0.5 m to 1.5 m above the terrain ground.
 15. The supporting structure of claim 1, comprising at least four module rails arranged in mutually parallel relationship.
 16. A method for installing a supporting structure having the structure of claim 1, comprising the steps of: securing the at least four vertical ground supports in the ground to form several parallel adjacent rows, with the free ends of the ground supports being located approximately at an identical height above terrain ground, connecting the plurality of beams to the free ends of those ground supports that are located next to one another at identical row positions along the rows, tensioning the at least one module rail by affixing one end of the module rail and applying a tensioning force to another end of the module rail, and attaching the at least one module rail to the plurality of beams under tension. 